1. Field of the Invention
The present invention relates to an apparatus for recording an image, and more particularly, it relates to an image recorder having an recording head and a light source which are separated from each other so that laser beams from the light source are guided to the recording head through an optical fiber cable.
2. Description of the Prior Art
In an image recorder, a light source is provided in the interior or exterior of a recording head on the recorder.
For example, Japanese Patent Laid-Open Gazette No. 14134/1983 discloses an image recorder having a light source exteriorly of a recording head. FIG. 1 illustrates a recording part of this image order. As shown in FIG. 1, a light source part 50 and a recording head 64 are separately provided and connected with each other through optical fiber cables 60.
The light source part 50 is comprises of a laser tube 52, an optical unit 54, for expanding a laser beam leaving the laser tube 52, in a direction (upper and lower direction in FIG. 1) perpendicular to an optical axis of the laser beam, an acoustic optical modulator system 56 comprising a plurality of optical modulators which are provided in correspondence to the laser beams of the optical unit 54 for independently turning the laser beam on-off in response to image signals corresponding to an image to be recorded, and condenser lenses 58 converging the respective laser beams from the acoustic optical modulator system 56 and introducing them into incident ends 62 of the optical fiber cables 60. Thus, the laser beams from the laser tube 52 are modulated in response to the image signals supplied to the light source part 50, and are thereafter guided to the recording head 64 through the plurality of optical fiber cables 60.
The recording head 64 comprises an image formation lens 68, so that the laser beams emerging from ends 66 of the optical fiber cables 60 are made to impinge onto a photosensitive material F which is wound on a rotating cylinder 2 through the image formation lens 68, respectively.
As understood from FIG. 1, the optical unit 54, the acoustic optical modulator system 56 and the condenser lenses 58 are provided in the optical paths for introducing the laser beams of outgoing from the laser tube 52 into the optical fiber cables 60, so that the optical path length l from the laser tube 52 to the incident ends of the optical fiber cables 60 is considerably long. Therefore, even if optical axes of the laser beams are only slightly changed due to changes in ambient temperature or vibration of the image recorder, the optical axes of the laser beams may be so displaced from those of the optical fiber cables 60 that the laser beams cannot be introduced into the optical fiber cables 60.
In order to overcome the problem, the optical fiber cables 60 have been generally constructed in the form of multimode optical fibers. This is because the core diameter of a multimode optical fiber cable is larger than that of a single mode fiber. That is, even if the optical axes of the laser beams are slightly displaced, the laser beams will nonetheless be coupled into the incident ends 62 of the optical fiber cables 60 since the optical fiber cables 60 have larger core diameters.
Multimode optical fiber cables 60 guide the laser beams mainly through internal irregular reflection within the fibers as is well known in the art. Thus, the laser beams of the optical fiber cables 60 have a speckled or spotted pattern, as shown in FIG. 2.
Therefore, when the optical fiber cables 60 are bent following movement of the recording head 64 during recording of an image on the photosensitive material F, the aforementioned spotted pattern will vary and cause fluctuations in the amounts of light of the respective laser beams incident upon the image formation lens 68, i.e., the exposure levels of the photosensitive material F will vary. Consequently, the diameters of the pixels recorded on the photosensitive material F will similarly vary which will deteriorate the picture quality.
According to the known art furthermore, the respective laser beams modulated by the acoustic optical modulator 56 are guided to the recording head 64 through the plurality of optical fiber cables 60 as described above, and hence a large number of elements are required for arranging the optical fiber cables, which increases the size of the apparatus, and complicates adjusting of the optical system etc.